Early Development of Direction Selectivity in the Higher Visual Cortex.

A fundamental aspect of visual motion processing is the computation of motion direction. In ferrets, as in primates, selectivity for motion direction is found both in early cortical stages like the primary visual cortex (V1) and in higher visual areas like the middle temporal area in primates and the posteromedial lateral suprasylvian (PMLS) area in ferrets. Little is known about how this critical tuning function develops in higher visual cortex. Here, by studying the development of the ferret's motion pathway, we first reveal the surprising finding that direction selectivity (DS) develops earlier in PMLS than in V1, contrary to the areas' hierarchical positions. Our data, collected in animals of either sex, furthermore show that while DS is sensitive to visual experience in both areas, the sensitivity profile differs between them: presentation of drifting gratings, containing the full complement of spatial and temporal cues generated by visual motion, can promote DS development in V1 and PMLS. In contrast, flashing stationary stimuli, which lack the spatial displacement of moving stimuli and only contain temporal changes, induce DS only in PMLS, not V1. Collectively our findings reveal significant deviations in PMLS development from that in V1, which will be important to account for in models of motion pathway development and of the developmental disorders that affect this pathway. The complex pattern of relative PMLS and V1 development also highlights the need to address interactions between areas in developmental research.